Propose mechanisms for the following reactions.
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Question

Propose mechanisms for the following reactions.

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Accepted Answer

Hi, everyone. Let's look at our next problem. It says, propose a suitable mechanism to show the, I mean formation in the given reaction. And when we look at the reaction that we're given, we see our reactant is a six carbon ring with two alcoy groups attached to one of its carbons. This is an ace and aces are derivatives of alde hydro aldehyde or ketones where instead of the Carboni bond, you have that carbon uh bond instead two alcoy groups. Uh This acetal is reacting with an amine under acidic conditions. The amine is in the form of uh NH three plus the nitrogen group, the nitrogen has a positive charge and the product is an, I mean, as our problem says, it means being those nitrogen analogs to carbon groups where you have ac double bond N instead of ac double bond O. So we need to propose a mechanism for this. And we can recall that aces just like aldehyde and ketones can react with amines to form amines through a condensation reaction. Those reactions that join two molecules with the elimination of a small molecule like water or alcohol. So let's see how we're going to do this. Our first step is going to be an acid catalyzed removal of one alcoy group to form a resonant stabilized Carbocaine. So we'll put that in there as our first step. So in our first step, here's our acetal and here's our amine with its positively charged nitrogen and three hydrogens. So the lone pair on one of these oxygens is going to snag a proton from our amine causing those electrons from that NH bond to come on to the forming lone pair on that positively charged nitrogen. So that's gonna lead to the formation of that positively charged Carbocaine when this alcoy group leaves. So now that we have this, we've protend this oxygen, our oxygen has a positive charge, which it's not happy with. So the electrons from the co bond that holds the alcoy Groupon are going to come on to the oxygen breaking that co bond so that we've gotten rid of one alcoy group and that's gonna leave a positive charge on the carbon atom. So let's take a look at what that looks like. So we're left with this Carbocaine here, we've had our first condensation reaction. Our carbon has a positive charge because it now only has three bonds and normally that wouldn't be a very stable arrangement. But in this case, because of the oxygen and the alcoy group, this is actually a resonance stabilized Carbocaine. So here's its other resonance structure, the lone pair of this oxygen can come down here to form a double bond between the C and the O putting the positive charge on oxygen, which it doesn't like very much. But again, it's stabilized by that resonance structure as you can break this double bond and put the loan pair back on the oxygen regenerating the carbo CAD ion. So that's your resonance structure there stabilizing our carbo CAD ion. So I'm just gonna remove these electron arrows to keep it. Uh So we can focus on the mechanism of our reaction here and look at our next step, which is going to involve an attack by our amine to form that CN first CN bond to lead to our amine. So now we see we've got the, our basic form of our aming here and the lone pair on that nitrogen comes over here to form a bond with that positively charged carbon in our Carbocaine form that's gonna lead to are nitrogen atom having a positive charge after the formation of that new bond. And it will react with the basic form of the amine. As the lone pair on that nitrogen detonates that nitrogen atom, the electrons from the NH bond then become a lone pair on the nitrogen. And we've now generated our alco amine intermediate. So now we've seen part two of our mechanism, the attack by the amine on the Carbocaine, the derotation of the nitrogen. We've gotten to alcoy amine intermediate, which is now going to be ready for a second acid catalyzed removal of the other alcoy group. So let's see how that happens. So, just as we saw in the first step, the lone pair on the oxygen of the cell coy group, we'll snag a proton from our acidic amine there, the electrons from that NH bond will come over here to become a lone pair on the nitrogen forming its conjugate base. And we've now turned our alcoy group into a leaving group ready for that second condensation reaction. So our oxygen atom now has a positive charge which is not a favorable arrangement. So the electrons from the co bond there go on to the oxygen as a lone pair and that generates another resonant stabilized Carbocaine. Though this time, uh the resonance structure will be with uh this CN bond rather than the co bond. So let's draw how that resonance structure looks. So that lone pair on the nitrogen can come and form a double bond with that positively charged carbon. And then those electrons could come back to the positively charged nitrogen to form our two resonance structures. Well, now you can see in the second resonance structure, there's that CN double bond that we're looking for in the end product with our. So I'm just gonna erase these arrows. So we can focus on our mechanism and look at our very last step, which will be the de protonation of the nitrogen to form our final product. So now we're looking at that resonance structure with the C and double bond, we're looking for our nitrogen has a positive charge. So we have a lone pair on this basic form of our D proin that nitrogen and the electrons from the NH bond go to be a lone pair on the nitrogen. And that's gonna give us our final immune product. So we've now generated our final immun product. We have that lone pair on the nitrogen through that second condensation reaction. And so we have our three basic steps of our mechanism. Uh The first part, the acid catalyzed removal of the first alcoy group. The second part being the attack by the amine and the de protonation of the nitrogen, we formed our alco amine intermediate. And then finally, the acid catalyzed removal of the second alcoy group with the derogation of the nitrogen. See you in the next video.

Propose mechanisms for the following reactions.
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Key Concepts

Nucleophilic Substitution Reactions

Mechanism of Amine Formation

Stereochemistry in Reactions

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